Stackable containers are conveyed in a state where a required number thereof are stacked, and when the containers are stored in a storage area of a conveyance destination of the container stack, for example, in a storage area where the containers are directly placed on a floor surface, it is effective to significantly enhance the floor surface utilization efficiency in a case where the containers are placed on the floor one by one. Also, when the containers are retrieved, since a plurality of containers stacked can be integrally retrieved as they are, a retrieval operation can be performed efficiently. As a matter of course, in the storage area for the container stack described above, an automatic storage/retrieval device for a container stack is equipped in which in a conveyance carriage capable of being moved horizontally at a constant height above the floor surface in an X-Y arbitrary direction, a transfer device capable of raising and lowering the container stack by gripping it laterally is provided. Although a patent literature disclosing this background art cannot be explicitly indicated, the present applicant has disclosed, in Japanese Patent Application Nos. 2015-92812 to 2015-92814 which are previous applications, the technical content in which the container stack described above is conveyed to and stored in the storage area.